Cause of the decreased number of PGC in albino Xenopus: analysis of the number and position of pPGC in albino embryos during and after cleavage.

In order to understand the cause for the decreased number of primordial germ cells (PGC) in Xenopus albino (a(p)/a(p)) tadpoles, the number of presumptive PGC (pPGC) in the albino and wild-type embryos at Nieuwkoop and Faber's stages 6-37/38 were examined using the antibody specific to germ plasm. The positions of pPGC in the endodermal cell mass in embryos of both types at stages 28 and 33/34 were also observed to learn the migratory behavior of pPGC. The number of pPGC in the albino increased up to stage 28 with development, but decreased thereafter. In contrast, the number in the wild-type increased to stage 33/34 as development proceeded, and the number of pPGC in stage 33/34 embryos reached nearly that of PGC of the feeding tadpoles in the same batches. Judging from the positions of pPGC, the migration of pPGC from the median part through the lateral to the dorsal part of the endodermal cell mass in the albino was suspected to be somewhat later than that in the wild-type. These results, together with the results in previous studies, suggest that the decreased number of PGC in the albino would be closely related to the sudden decrease in number of pPGC at stage 33/34, as well as to the ectopic position of pPGC in endodermal cell mass, the latter of which had already been demonstrated to be responsible for the differentiation into PGC.